It looks like a magenta color compensating filter, a fairly strong one, perhaps about a CC40M or so, although filter colors are hard to judge from a picture. I don't have an idea of why Kodak would have labeled it "MC1".
I have a Kodak photo handbook from 1946 and they list color compensating filters as CC3, CC4, CC5, CC6, etc rather than the modern terminology of CC - number of units - color letter (ie C,M,Y,R,G,B). They don't list any filters named MC in 1946.
Magenta CC filters are pretty close to the harder grades of variable contrast paper filtering, but Kodak never called variable contrast paper "MC" to my knowledge. It's certainly not "grade 1" which would usually be a yellow filter.
I don't think this would be particularly useful as a taking-lens filter unless you need to photograph in very greenish light. If you wish to boost contrast in B&W photography, a yellow, orange, or red filter (or sometimes green) is useful.